As n2oiroc said, be sure to 'seat' the belt prior to checking if it's at the proper sheave height. Once I install a belt, it always sits way down, that's because the two sheave halves have not come together (because the belts sitting way too low). Do this, lock the parking brake to keep the secondary from turning, with your left hand, grab the belt where it sits in the primary and cinch it to keep it from turning. Now, with your right hand, grab the helix (angled ramps) on the face of the secondary and try pushing in on it to force the belt up as high as it will go on the secondary. With your left hand, you may have to push the belt a bit from the primary in the direction of the secondary to get every little bit of slack out of the belt. Keep doing this as it will keep allowing your belt to ride higher and higher onto the sheaves. If it's a new belt and you have the proper washer/bolts, it will sit between the specs of 1.5 (+-) on the sheaves.
Jon